diff --git a/src/Composer/Autoload/PhpFileCleaner.php b/src/Composer/Autoload/PhpFileCleaner.php
index 9b0872aad..4d8944e00 100644
--- a/src/Composer/Autoload/PhpFileCleaner.php
+++ b/src/Composer/Autoload/PhpFileCleaner.php
@@ -54,6 +54,9 @@ class PhpFileCleaner
         $this->maxMatches = $maxMatches;
     }
 
+    /**
+     * @return string
+     */
     public function clean()
     {
         $clean = '';
@@ -212,11 +215,17 @@ class PhpFileCleaner
         }
     }
 
+    /**
+     * @return bool
+     */
     private function peek($char)
     {
         return $this->index + 1 < $this->len && $this->contents[$this->index + 1] === $char;
     }
 
+    /**
+     * @return bool
+     */
     private function match($regex, array &$match = null)
     {
         if (\preg_match($regex, $this->contents, $match, 0, $this->index)) {
diff --git a/src/Composer/Cache.php b/src/Composer/Cache.php
index 8ee724357..b6fcf17e7 100644
--- a/src/Composer/Cache.php
+++ b/src/Composer/Cache.php
@@ -75,11 +75,17 @@ class Cache
         return $this->readOnly;
     }
 
+    /**
+     * @return bool
+     */
     public static function isUsable($path)
     {
         return !preg_match('{(^|[\\\\/])(\$null|nul|NUL|/dev/null)([\\\\/]|$)}', $path);
     }
 
+    /**
+     * @return bool
+     */
     public function isEnabled()
     {
         if ($this->enabled === null) {
@@ -97,11 +103,17 @@ class Cache
         return $this->enabled;
     }
 
+    /**
+     * @return string
+     */
     public function getRoot()
     {
         return $this->root;
     }
 
+    /**
+     * @return string|false
+     */
     public function read($file)
     {
         if ($this->isEnabled()) {
@@ -116,6 +128,9 @@ class Cache
         return false;
     }
 
+    /**
+     * @return bool
+     */
     public function write($file, $contents)
     {
         if ($this->isEnabled() && !$this->readOnly) {
@@ -154,6 +169,7 @@ class Cache
 
     /**
      * Copy a file into the cache
+     * @return bool
      */
     public function copyFrom($file, $source)
     {
@@ -175,6 +191,7 @@ class Cache
 
     /**
      * Copy a file out of the cache
+     * @return bool
      */
     public function copyTo($file, $target)
     {
@@ -198,6 +215,9 @@ class Cache
         return false;
     }
 
+    /**
+     * @return bool
+     */
     public function gcIsNecessary()
     {
         if (self::$cacheCollected) {
@@ -216,6 +236,9 @@ class Cache
         return !mt_rand(0, 50);
     }
 
+    /**
+     * @return bool
+     */
     public function remove($file)
     {
         if ($this->isEnabled()) {
@@ -228,6 +251,9 @@ class Cache
         return false;
     }
 
+    /**
+     * @return bool
+     */
     public function clear()
     {
         if ($this->isEnabled()) {
@@ -239,6 +265,9 @@ class Cache
         return false;
     }
 
+    /**
+     * @return bool
+     */
     public function gc($ttl, $maxSize)
     {
         if ($this->isEnabled()) {
@@ -269,6 +298,9 @@ class Cache
         return false;
     }
 
+    /**
+     * @return string|false
+     */
     public function sha1($file)
     {
         if ($this->isEnabled()) {
@@ -281,6 +313,9 @@ class Cache
         return false;
     }
 
+    /**
+     * @return string|false
+     */
     public function sha256($file)
     {
         if ($this->isEnabled()) {
@@ -293,6 +328,9 @@ class Cache
         return false;
     }
 
+    /**
+     * @return Finder
+     */
     protected function getFinder()
     {
         return Finder::create()->in($this->root)->files();
diff --git a/src/Composer/Command/ArchiveCommand.php b/src/Composer/Command/ArchiveCommand.php
index 3acf4fd04..379781a68 100644
--- a/src/Composer/Command/ArchiveCommand.php
+++ b/src/Composer/Command/ArchiveCommand.php
@@ -16,6 +16,7 @@ use Composer\Factory;
 use Composer\IO\IOInterface;
 use Composer\Config;
 use Composer\Composer;
+use Composer\Package\BasePackage;
 use Composer\Package\CompletePackageInterface;
 use Composer\Repository\CompositeRepository;
 use Composer\Repository\RepositoryFactory;
@@ -108,6 +109,9 @@ EOT
         return $returnCode;
     }
 
+    /**
+     * @return int
+     */
     protected function archive(IOInterface $io, Config $config, $packageName = null, $version = null, $format = 'tar', $dest = '.', $fileName = null, $ignoreFilters = false, Composer $composer = null)
     {
         if ($composer) {
@@ -142,7 +146,7 @@ EOT
     }
 
     /**
-     * @return CompletePackageInterface|false
+     * @return BasePackage&CompletePackageInterface|false
      */
     protected function selectPackage(IOInterface $io, $packageName, $version = null)
     {
diff --git a/src/Composer/Command/ConfigCommand.php b/src/Composer/Command/ConfigCommand.php
index 39b4604d3..c96597dce 100644
--- a/src/Composer/Command/ConfigCommand.php
+++ b/src/Composer/Command/ConfigCommand.php
@@ -58,9 +58,6 @@ class ConfigCommand extends BaseCommand
      */
     protected $authConfigSource;
 
-    /**
-     * {@inheritDoc}
-     */
     protected function configure()
     {
         $this
@@ -148,9 +145,6 @@ EOT
         ;
     }
 
-    /**
-     * {@inheritDoc}
-     */
     protected function initialize(InputInterface $input, OutputInterface $output)
     {
         parent::initialize($input, $output);
@@ -204,9 +198,6 @@ EOT
         }
     }
 
-    /**
-     * {@inheritDoc}
-     */
     protected function execute(InputInterface $input, OutputInterface $output)
     {
         // Open file in editor
diff --git a/src/Composer/Command/CreateProjectCommand.php b/src/Composer/Command/CreateProjectCommand.php
index b64b01e18..e47945466 100644
--- a/src/Composer/Command/CreateProjectCommand.php
+++ b/src/Composer/Command/CreateProjectCommand.php
@@ -159,6 +159,9 @@ EOT
         );
     }
 
+    /**
+     * @return int
+     */
     public function installProject(IOInterface $io, Config $config, InputInterface $input, $packageName, $directory = null, $packageVersion = null, $stability = 'stable', $preferSource = false, $preferDist = false, $installDevPackages = false, $repositories = null, $disablePlugins = false, $noScripts = false, $noProgress = false, $noInstall = false, $ignorePlatformReqs = false, $secureHttp = true, $addRepository = false)
     {
         $oldCwd = getcwd();
@@ -304,6 +307,9 @@ EOT
         return 0;
     }
 
+    /**
+     * @return bool
+     */
     protected function installRootPackage(IOInterface $io, Config $config, $packageName, $directory = null, $packageVersion = null, $stability = 'stable', $preferSource = false, $preferDist = false, $installDevPackages = false, array $repositories = null, $disablePlugins = false, $noScripts = false, $noProgress = false, $ignorePlatformReqs = false, $secureHttp = true)
     {
         if (!$secureHttp) {
diff --git a/src/Composer/Command/DiagnoseCommand.php b/src/Composer/Command/DiagnoseCommand.php
index 4f5eefeb3..b788c5e0f 100644
--- a/src/Composer/Command/DiagnoseCommand.php
+++ b/src/Composer/Command/DiagnoseCommand.php
@@ -65,9 +65,6 @@ EOT
         ;
     }
 
-    /**
-     * {@inheritdoc}
-     */
     protected function execute(InputInterface $input, OutputInterface $output)
     {
         $composer = $this->getComposer(false);
@@ -195,6 +192,9 @@ EOT
         return $this->exitCode;
     }
 
+    /**
+     * @return string|true
+     */
     private function checkComposerSchema()
     {
         $validator = new ConfigValidator($this->getIO());
@@ -219,6 +219,9 @@ EOT
         return true;
     }
 
+    /**
+     * @return string|true
+     */
     private function checkGit()
     {
         if (!function_exists('proc_open')) {
@@ -233,6 +236,9 @@ EOT
         return true;
     }
 
+    /**
+     * @return string|string[]|true
+     */
     private function checkHttp($proto, Config $config)
     {
         $result = $this->checkConnectivity();
@@ -268,6 +274,9 @@ EOT
         return true;
     }
 
+    /**
+     * @return string|true|\Exception
+     */
     private function checkHttpProxy()
     {
         $result = $this->checkConnectivity();
@@ -293,6 +302,9 @@ EOT
         return true;
     }
 
+    /**
+     * @return string|true|\Exception
+     */
     private function checkGithubOauth($domain, $token)
     {
         $result = $this->checkConnectivity();
@@ -322,7 +334,7 @@ EOT
      * @param  string             $domain
      * @param  string             $token
      * @throws TransportException
-     * @return array|string
+     * @return mixed|string
      */
     private function getGithubRateLimit($domain, $token = null)
     {
@@ -341,6 +353,9 @@ EOT
         return $data['resources']['core'];
     }
 
+    /**
+     * @return string|true
+     */
     private function checkDiskSpace($config)
     {
         $minSpaceFree = 1024 * 1024;
@@ -353,6 +368,9 @@ EOT
         return true;
     }
 
+    /**
+     * @return string[]|true
+     */
     private function checkPubKeys($config)
     {
         $home = $config->get('home');
@@ -382,6 +400,9 @@ EOT
         return $errors ?: true;
     }
 
+    /**
+     * @return string|\Exception|true
+     */
     private function checkVersion($config)
     {
         $result = $this->checkConnectivity();
@@ -403,6 +424,9 @@ EOT
         return true;
     }
 
+    /**
+     * @return string
+     */
     private function getCurlVersion()
     {
         if (extension_loaded('curl')) {
@@ -469,6 +493,9 @@ EOT
         }
     }
 
+    /**
+     * @return string|true
+     */
     private function checkPlatform()
     {
         $output = '';
@@ -699,7 +726,7 @@ EOT
     /**
      * Check if allow_url_fopen is ON
      *
-     * @return true|string
+     * @return string|true
      */
     private function checkConnectivity()
     {
diff --git a/src/Composer/Command/HomeCommand.php b/src/Composer/Command/HomeCommand.php
index 1a228b871..62c52e923 100644
--- a/src/Composer/Command/HomeCommand.php
+++ b/src/Composer/Command/HomeCommand.php
@@ -97,6 +97,9 @@ EOT
         return $return;
     }
 
+    /**
+     * @return bool
+     */
     private function handlePackage(CompletePackageInterface $package, $showHomepage, $showOnly)
     {
         $support = $package->getSupport();
@@ -122,6 +125,7 @@ EOT
      * opens a url in your system default browser
      *
      * @param string $url
+     * @return void
      */
     private function openBrowser($url)
     {
@@ -129,7 +133,8 @@ EOT
 
         $process = new ProcessExecutor($this->getIO());
         if (Platform::isWindows()) {
-            return $process->execute('start "web" explorer ' . $url, $output);
+            $process->execute('start "web" explorer ' . $url, $output);
+            return;
         }
 
         $linux = $process->execute('which xdg-open', $output);
diff --git a/src/Composer/Command/InitCommand.php b/src/Composer/Command/InitCommand.php
index c8888f07e..469df7ffb 100644
--- a/src/Composer/Command/InitCommand.php
+++ b/src/Composer/Command/InitCommand.php
@@ -461,7 +461,7 @@ EOT
     /**
      * @private
      * @param  string $author
-     * @return array
+     * @return array{name: string, email: string}
      */
     public function parseAuthorString($author)
     {
@@ -485,6 +485,9 @@ EOT
         return $this->getRepos()->search($name);
     }
 
+    /**
+     * @return CompositeRepository
+     */
     protected function getRepos()
     {
         if (!$this->repos) {
@@ -663,6 +666,9 @@ EOT
         return $requires;
     }
 
+    /**
+     * @return array<int, array{name: string, email: string}>
+     */
     protected function formatAuthors($author)
     {
         return array($this->parseAuthorString($author));
@@ -775,6 +781,9 @@ EOT
         file_put_contents($ignoreFile, $contents . $vendor. "\n");
     }
 
+    /**
+     * @return bool
+     */
     protected function isValidEmail($email)
     {
         // assume it's valid if we can't validate it
@@ -790,6 +799,9 @@ EOT
         return false !== filter_var($email, FILTER_VALIDATE_EMAIL);
     }
 
+    /**
+     * @return RepositorySet
+     */
     private function getRepositorySet(InputInterface $input, $minimumStability = null)
     {
         $key = $minimumStability ?: 'default';
@@ -802,6 +814,9 @@ EOT
         return $this->repositorySets[$key];
     }
 
+    /**
+     * @return string
+     */
     private function getMinimumStability(InputInterface $input)
     {
         if ($input->hasOption('stability')) {
@@ -936,6 +951,9 @@ EOT
         );
     }
 
+    /**
+     * @return string
+     */
     private function getPlatformExceptionDetails(PackageInterface $candidate, PlatformRepository $platformRepo = null)
     {
         $details = array();
@@ -993,6 +1011,9 @@ EOT
         return array_keys(array_slice($similarPackages, 0, 5));
     }
 
+    /**
+     * @return void
+     */
     private function updateDependencies($output)
     {
         try {
@@ -1004,6 +1025,9 @@ EOT
         }
     }
 
+    /**
+     * @return void
+     */
     private function runDumpAutoloadCommand($output)
     {
         try {
@@ -1015,6 +1039,9 @@ EOT
         }
     }
 
+    /**
+     * @return bool
+     */
     private function hasDependencies($options)
     {
         $requires = (array) $options['require'];
diff --git a/src/Composer/Command/RequireCommand.php b/src/Composer/Command/RequireCommand.php
index ad65420af..9388af63d 100644
--- a/src/Composer/Command/RequireCommand.php
+++ b/src/Composer/Command/RequireCommand.php
@@ -417,6 +417,9 @@ EOT
         return $status;
     }
 
+    /**
+     * @return bool
+     */
     private function updateFileCleanly($json, array $new, $requireKey, $removeKey, $sortPackages)
     {
         $contents = file_get_contents($json->getPath());
diff --git a/src/Composer/Command/RunScriptCommand.php b/src/Composer/Command/RunScriptCommand.php
index 81b625786..052139f8b 100644
--- a/src/Composer/Command/RunScriptCommand.php
+++ b/src/Composer/Command/RunScriptCommand.php
@@ -109,6 +109,9 @@ EOT
         return $composer->getEventDispatcher()->dispatchScript($script, $devMode, $args);
     }
 
+    /**
+     * @return int
+     */
     protected function listScripts(OutputInterface $output)
     {
         $scripts = $this->getComposer()->getPackage()->getScripts();
diff --git a/src/Composer/Command/SelfUpdateCommand.php b/src/Composer/Command/SelfUpdateCommand.php
index 70e65d252..bfa1bd481 100644
--- a/src/Composer/Command/SelfUpdateCommand.php
+++ b/src/Composer/Command/SelfUpdateCommand.php
@@ -369,6 +369,9 @@ TAGSPUBKEY
         $io->write('Public keys stored in '.$config->get('home'));
     }
 
+    /**
+     * @return int
+     */
     protected function rollback(OutputInterface $output, $rollbackDir, $localFilename)
     {
         $rollbackVersion = $this->getLastBackupVersion($rollbackDir);
@@ -464,6 +467,9 @@ TAGSPUBKEY
         }
     }
 
+    /**
+     * @return string|false
+     */
     protected function getLastBackupVersion($rollbackDir)
     {
         $finder = $this->getOldInstallationFinder($rollbackDir);
@@ -477,6 +483,9 @@ TAGSPUBKEY
         return false;
     }
 
+    /**
+     * @return Finder
+     */
     protected function getOldInstallationFinder($rollbackDir)
     {
         return Finder::create()
diff --git a/src/Composer/Command/UpdateCommand.php b/src/Composer/Command/UpdateCommand.php
index 0fe582299..7c2a7dcee 100644
--- a/src/Composer/Command/UpdateCommand.php
+++ b/src/Composer/Command/UpdateCommand.php
@@ -304,6 +304,9 @@ EOT
         throw new \RuntimeException('Installation aborted.');
     }
 
+    /**
+     * @return Link
+     */
     private function appendConstraintToLink(Link $link, $constraint)
     {
         $parser = new VersionParser;
diff --git a/tests/Composer/Test/Autoload/AutoloadGeneratorTest.php b/tests/Composer/Test/Autoload/AutoloadGeneratorTest.php
index 0e571f81a..521e762fb 100644
--- a/tests/Composer/Test/Autoload/AutoloadGeneratorTest.php
+++ b/tests/Composer/Test/Autoload/AutoloadGeneratorTest.php
@@ -1737,6 +1737,9 @@ EOF;
         }
     }
 
+    /**
+     * @return array<string, mixed[]>
+     */
     public function platformCheckProvider()
     {
         $versionParser = new VersionParser();